3个7 1个2怎么算29

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3个71个2怎么算293个71个2怎么算293个71个2怎么算29这个只用加减乘除没法算的1/x(4-x)=-(1/4)*4/(x-4)x=-(1/4)*[x-(x-4)]/(x-4)x=-(1/4)

3个7 1个2怎么算29
3个7 1个2怎么算29

3个7 1个2怎么算29
这个只用加减乘除没法算的

1/x(4-x)
=-(1/4)*4/(x-4)x
=-(1/4)*[x-(x-4)]/(x-4)x
=-(1/4)*[x/(x-4)x-(x-4)/(x-4)x]
=-(1/4)*[1/(x-4)-1/x]
所以原式=(-1/4)∫[1/(x-4)-1/x]dx
=(-1/4)(ln|x-4|-ln|x|)+C